Pena (illness) will begin a rehab assignment with the Brewers' Arizona Complex League affiliate Friday, Todd Rosiak of the Milwaukee Journal Sentinel reports.
Pena hasn't played since April 22, when he collapsed in the dugout at High-A Wisconsin after becoming overheated. It shouldn't be long before Pena rejoins the active roster at Wisconsin, where he's slashed .372/.462/.512 in 12 games this season.